A full suspension Muni. Several have built ones that effectively only suspend the seat, but none have made a fulll sus.
A lot of interesting ideas in this thread.
http://www.unicyclist.com/forums/showthread.php?t=32510&highlight=full+suspension
Learning aid - Justonewheel.com buit a device that you bolt to the bottom of the frame in place of the bearing caps.
Fixed gear set up that would be easy to mass produce. A few on hear have built their own including one w/ a chain drive on a 26".